What is define in php

define in php is a function used to define constants. Constants refer to values ​​that cannot be changed or redefined. Unlike variables, once a constant is defined, it cannot be modified or revoked. Its function syntax is "define (name, value, case_insensitive)", it should be noted that constant names usually follow certain specifications, such as using all uppercase letters, using underscores _ to separate words, etc.

Operating system for this tutorial: Windows 10 system, php8.1.3 version, Dell G3 computer.

define in php is a function used to define constants

Constant refers to a value that cannot be changed or redefined. Unlike variables, constants cannot be modified or undone once defined

Syntax and parameters of the "define()" function:

define(name, value, case_insensitive)

• name: constant name (such as MY_CONST)

• value: value of the constant (such as 1234)

• case_insensitive: optional parameter, if set to true, it means that this constant is not case-sensitive, and the default is false.

The code example is as follows:

define("PI", 3.14);
define("GREETING", "Hello World!");
echo PI; // 输出 3.14
echo GREETING; // 输出 Hello World!

It should be noted that constant names usually follow certain specifications, such as using all uppercase letters and using underscores _ to separate words etc.

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